1. Field of the Invention
The present invention relates to a fuel supply apparatus, and in particular, to a pulsation reducing structure of a fuel supply apparatus for reducing pulsation generated by an operation of a pressure regulator.
2. Description of Related Art
The pressure of fuel supplied to a high pressure pump has been conventionally reduced below a predetermined pressure by disposing a pressure regulator in the low pressure fuel passage for supplying the fuel pumped out from a fuel tank by the low pressure pump to the high pressure pump or in the low pressure fuel passage disposed in the high pressure pump.
However, when the valve member of the pressure regulator is lifted by the pressure of fuel to discharge the fuel, an opening between the valve member and a valve seat is disposed under negative pressure, and such negative pressure produces cavitation in the fuel. When such cavitation disappears, a large pressure wave is generated. Therefore, if the pressure wave is repeatedly generated according to the opening and the closing of the pressure regulator, it may cause a pressure pulsation.
The pressure pulsation generated by the pressure regulator is transmitted in the fuel pipe for supplying the low pressure fuel to the high pressure pump, and produces noises. In particular, if a fuel filter is disposed in the fuel pipe which connects a low pressure pump and the high pressure pump, and is mounted to a vehicle body, the vibration of the fuel filter caused by the pressure pulsation is transmitted to the vehicle body and cause large noise in the car.
A pulsation damper of diaphragm type may be connected to the fuel pipe to reduce such pressure pulsation. However, the frequency of the pressure pulsation generated by the pressure regulator is high, and the pulsation damper of diaphragm type can not respond to such high frequency of the pressure pulsation. Furthermore, if the amplitude of the pressure pulsation is large, it may be a problem that the diaphragm may be broken.